Physical Properties of Water

Title: Physical properties of water

Aim: To determine the factors that affect the boiling rate and boiling point of water as well as the effect of varying relative humilities on the water activity of foods.

Results

Part A

Figure1: Graph of temperature against time in different volume of water.

Part B

Figure 2: Graph of temperature against time in pure water and water with solute.

Discussion Question:

Part A

1. Yes, the curves in part a (i), (ii), (iii) have a flat section. Once the water reaches its boiling point, any additional heat will convert liquid to gas but the temperature still remains constant at its boiling point, which causes a flat section in the curves.

2. No. The boiling point of water should be same. The amount of water will not affect the boiling point of the water as it the boiling point of water depends on how much heat is required to vaporize the water, where the amount of heat required is affected by the altitudes and the addition of solutes.

3. 100ml of water will boil faster because small amount of water needs lesser thermal energy to reach the boiling point.

Part B

1. Water consists of NaCl has the highest boiling point. Addition of solute is one of the factors that will affect the boiling point. When a solute is dissolved in water, the vapour pressure is lowered (Barghouthi & Tullis, 2000). Boiling occurs when the vapour pressure of the solution is equal to atmospheric pressure. Therefore, the temperature must be higher than the normal boiling point of water in order to have a vapour pressure equal to the atmospheric pressure.

2. NaCl increases more on the boiling point of water. 10g of NaCl will give a higher moles of 10g of sucrose as the molar mass of NaCl is 58.4g/mol and the molar mass of sucrose is 342g/mol. Besides that, each NaCl molecules will split into two ions, which is the Na+ ions and Cl- ions, increasing the number of particles present in the water but sucrose does not ionize. NaCl has twice the number of particles in solution and forms a solution with a higher boiling point (Silver, 2005)

Conclusion:

The lesser the amount of water, the higher the boiling rate. Addition of solutes is one of the factors that affect the boiling point of the solution by reducing the vapour pressure.

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